In JavaScript, undefined is the default value for variables that have been declared but not initialized. On the other hand, null is an intentional assignment that explicitly indicates the absence of a value. Methods to Check if a Variable is Undefined Using typeof Operator Using Strict Equality...
Check if a Value IsNaNby Using a Comparison Operator in JavaScript The following method is even faster than the ones detailed above, and it also requires less code. On the other hand, it is a bit more confusing, not to mention that it may prove to be hard to maintain and document prop...
A variable is calledundefinedif it is declared without being assigned an initial value. Below are multiple ways we can do this in JavaScript. Directly Compare a Variable Withundefinedto Check Undefined in JavaScript varx;if(x===undefined){text='x is undefined';}else{text='x is defined';}...
It is used to represent the absence of a value. It get assigned to a variable when it is declared but not assigned any value. How to check if a variable is undefined?There are more than one way to check if a variable is undefined or not. Let's see them one by one. Using typeof...
This is why it’s better to use thetypeofoperator to really check if a value isundefined. Thetypeofoperator won’t throw an error when you haven’t declared the variable during the checking, but a direct comparison such asy === undefinedwill break your JavaScript application. ...
In JavaScript, a value can either be a primitive or an object. Therefore, you can check if a value is a JavaScript primitive (as opposed to being an object) using the following check: !(value instanceof Object) You may see value !== Object(value) as a means to check for prim...
Null or undefined value! Though, we don't really know which one of these is it. If we were to use the strict operator, which checks if a is null, we'd be unpleasantly surprised to run into an undefined value in the console.log() statement: let a; if (a === null) { console...
str2 = 'That is your place.' str3 = new String('Great Place'); Now to check whether a given variable is a string or not, we'll use a JavaScript operator calledtypeof. Syntax: typeof variable; This operator returns the data type of the variable specified after it. If the variable ...
If the value exists, then the function will return the index value of the element, else it will return -1 Syntax put-array-or-string-here.indexOf() Code //code to check if a value exists in an array using javascript indexOf var fruits_arr = ['Apple', 'Mango', 'Grapes', '...
If you don't want it to throw a TypeError, you can add an extra check:let value; value // 👈 null and undefined check && Object.keys(value).length === 0 && value.constructor === Object; value = null; // null value = undefined; // undefined ...